Low Carb for Type 1 Diabetes

iStock-1295633127"The source and amount of carbohydrates consumed affect postprandial hyperglycemia and glycemic variability more than any other dietary factor, providing a conceptual basis for interest in carbohydrate-modified diets for T1DM.” (Lennerz et al., 2018)

Among all cases of diabetes in the US, people with type 1 diabetes (T1D) account for just 6%, compared to over 90% having type 2. However, 6% of the total encompasses approximately 1.25 million people, so this is not a small number. Helping this population achieve stable blood glucose levels within a healthy range would have powerful beneficial effects on long-term health and quality of life. Prior to the discovery and widespread use of insulin, carbohydrate-restricted diets were the strongest known interventions for prolonging lifespan and delaying diabetic complications in these patients. The growing popularity of ketogenic diets in the modern era has spurred an expansion in clinical research on the safety and efficacy of keto for T1D. (Carbohydrate restriction has already been shown to put type 2 diabetes into remission and to reverse metabolic syndrome.)

Medical professionals and T1D patients alike may be trepidatious about using ketogenic diets (KDs) owing to confusion between nutritional ketosis and diabetic ketoacidosis. However, as we explained in a past article, the nutritional ketosis induced by dietary carbohydrate restriction is a world apart from the pathological ketoacidosis resulting from poorly controlled diabetes. In a well-formulated KD, there is very little risk of acidosis (except in individuals using SGLT2 inhibiting drugs). This confusion has precluded some professionals from recommending KDs to their patients even as the standard advice to follow a more “balanced” diet and cover the carbohydrate and protein with insulin typically results in a high degree of instability in blood sugar, with periods of extreme hyperglycemia and dangerous hypoglycemia. 

Some medical professionals and guideline-issuing organizations prefer to err on the side of caution and recommend lower insulin doses to prevent hypoglycemia. This means that these patients will have sustained blood glucose levels that are higher than might be desirable, and be at greater risk for the long-term consequences that come from this, such as eye, kidney, and nerve damage, as well as declining cognition, heart attack, stroke, and early mortality.

On the other hand, patients who choose to use higher doses of insulin to drive blood glucose lower may suffer negative consequences from chronic hyperinsulinemia. As they become more resistant to injected insulin and require increasingly higher doses, people with T1D may ultimately experience signs and symptoms of type 2 diabetes (T2D) or insulin resistance, such as weight gain, dyslipidemia, and hypertension. The development of insulin resistance resembling that seen in T2D among individuals with T1D is referred to as double diabetes.” In this scenario, high doses of insulin result in improved HbA1c, but this comes at the expense of increased risk for other, possibly more severe health complications.

Type 1 diabetics have not been served by casual advice to “carb up and shoot up” (with insulin). Evidence is mounting that very low-carb diets can substantially reduce the amount of insulin required while also reducing hypoglycemic events and blood sugar instability overall. This is what Dr. Richard K. Bernstein, a physician with T1D and author of Dr. Bernstein’s Diabetes Solution: The Complete Guide to Achieving Normal Blood Sugars, calls “the law of small numbers.” When less insulin is needed (owing to a lower carbohydrate intake), there is less volatility and unpredictability in the body’s response to it.

Motivated and educated patients sometimes take it upon themselves to adopt lower-carb or ketogenic diets with the goal of maintaining healthy blood glucose levels while employing lower doses of insulin. A survey of such patients was published in the journal Pediatrics in 2018 and became the journal’s most downloaded paper of that year. Self-reported mean daily carb intake among respondents was just 36g ±15g. Mean HbA1c was 5.67, and among participants who reported data from continuous glucose monitors (CGMs), average blood glucose was 104 ± 16 mg/dL. These numbers would be admirable even among individuals without diabetes, so it’s especially remarkable to see them among those with T1D, in whom blood sugar control is notoriously difficult. It’s even more impressive that this was achieved with average daily insulin doses of just 0.40 ± 0.19 units/kg—far less than many people with either type 1 or type 2 diabetes regularly employ. The study authors wrote:

“…we observed measures of glycemic control in the near-normal range, low rates of hypoglycemia and other adverse events, and generally high levels of satisfaction with health and diabetes control. These findings are without precedent among people with T1DM, revealing a novel approach to the prevention of long-term diabetes complications.”

The bulk of research on carbohydrate restriction in general, and KDs in particular, for T1D has mixed findings. This is likely because “low-carbohydrate” is a relative term. (Some studies on carbohydrate restriction employ diets with nearly 40% carbohydrate, while others are as low as 30g/day. This degree of heterogeneity makes it difficult to come to solid conclusions.) Some of the leading researchers in the field suggested using the American Diabetes Association’s cutoff of 130g/day (or < 26% of total calories) for a “low-carbohydrate diet” and defined a “very low-carbohydrate ketogenic diet” as 20-50g carbohydrate per day or < 10% of total calories from carbs whether or not ketosis occurs. However, there may be physiological effects that occur when carbs are kept closer to 5% of total calories rather than 25%, which makes for heterogeneous research results.

Several studies do indicate, however, that reducing dietary carbohydrate can have beneficial effects on glycemic control in T1D. It doesn’t always lead to significant reductions in HbA1b, but it typically reduces the frequency of hypoglycemic episodes and the magnitude of glycemic excursions throughout the day. The increased stability of blood sugar levels could potentially improve quality of life even if those levels are still elevated.

A pilot study is currently underway in Australia using a low-carb diet (<100g/day) in T1D, but a leading expert whose research helped to resurrect interest in KDs nearly two decades ago has proposed using a stricter approach (30g/day) to ensure that the shift to a ketogenic metabolism would be induced. It’s possible that the not-insignificant difference between a truly ketogenic diet versus a more liberal “low-carb” diet could mean the difference between increased stability of blood glucose and improved HbA1c while using less insulin, versus the relatively lackluster results seen in trials where carb intake was more generous.